An epitaxial growth technique that enables to form a film by vapor-depositing a single crystal thin film on a substrate is conventionally used at a manufacturing step of a semiconductor element that requires a crystal film with a relatively large thickness, as a power device such as an IGBT (Insulated Gate Bipolar Transistor).
In a film forming apparatus used for the epitaxial growth technique, a substrate is placed inside a film forming chamber that is kept at a normal pressure or a reduced pressure and a source gas and a doping gas are supplied into the film forming chamber while the substrate is rotated and heated. Accordingly, a pyrolytic reaction and a hydrogen reduction reaction of the source gas occur on the surface of the substrate and an epitaxial film is formed on the substrate.
The source gas and the doping gas are introduced from a gas supplier that is provided in an upper part of the film forming apparatus. However, if the source gas or the doping gas stays near a supply port of the gas supplier and is heated, a source or a dopant adheres to the surface of the gas supplier. If the source or the dopant having adhered to the gas supplier becomes particles and falls on the substrate, a defect may occur. Furthermore, the dopant having adhered to the gas supplier gasifies in the film forming chamber even when the gases in the film forming chamber are discharged or the film forming chamber is purged. In this case, discharge of the gases or purge of the film forming chamber takes a long time.